Abstract

Previous radiolarian zonations for the Late Cretaceous and Paleocene of Japan are reviewed in terms of species identification and age determinations. With adoption of a consistent identification scheme, a remarkably uniform succession of radiolarian assemblages is evident throughout Southwest Japan. Sufficient species range into higher northern latitudes (Hokkaido, eastern Russia) to permit the establishment of a single radiolarian zonation for the Northwest Pacific. The new zonation consists of six Late Cretaceous and two Paleocene interval zones: Theocampe urna zone (Tu, Coniacian), Dictyomitra koslovae zone (Dk, Santonian to earl Campanian), Amphipyndax tylotus zone (At, late Campanian), Pseudotheocampe abschnitta zone (Pa, early Maastrichtian), Clathrocyclas gravis zone (Cg, mid-Maastrichtian), Lithostrobus wero zone (Lw, early Paleocene), Buryella foremanae zone (Bf, mid-Paleocene). Zone Dk may be subdivided into Santonian and early Campanian subzones based on the first appearances of Archaeospongoprunum hueyi gr., Protoxiphotractis perplexus and Lithocampe wharanui. Previous workers' recognition of an Amphipyndax pseudoconulus or A. enesseffi assemblage in Japan is found to be erroneous. Careful examination of illustrations of the A. pseudoconulus-tylotus complex reveals that A. pseudoconulus s.s. (= A. enesseffi of Foreman 1966) is very rare in Japan and restricted to the late Campanian, its first appearance coinciding with that of A. tylotus.